Method of halogenating cyclohexane



5 194g@ I E Q, BRlTTQN ETAL METHOD OF HALOGENATING CYCLOHEX'A'NE ATTORNE w Patented `une 23, 1942 sra'rss METHOD OF HALOGENTING CYCLOHEXANE gall Application March 9, 1938, Serial No. 194,916

2 Claims.

This invention concerns an improved method of halogenating cyclohexaneto obtain a desired monohaloor polyhalo-cyclohexane as the majorproduct. It particularly concerns the manufacture ofmonochloro-cyclohexane, i. e. cyclohexyl chloride, by directchlorination of cyclohexane.

Cyclohexyl chloride and cyclohexyl bromide have heretofore been preparedby two general methods, viz.; direct halogenation of cyclohexane andreaction of hydrochloric or hydrobromic acid with cyclohexanol. Themethod involving direct halogenation of cyclohexane has found little, ifany, commercial application due to the fact that polyhalo-cyclohexanesare formed in considerable yield when the halogenation is carried farenough for practical operation. For instance, Markownikoi, Ann. 302, 9(1898), has shown that when cyclohexane is reacted in batch manner withnot over 50 per cent of its molecular equivalent of chlorine, theproduct consists largely of polychloro-cyclohexane. Sabatier and Maihle,Compte Rendus 137, 240 (1903), carried the reaction out at C., under thecatalytic action of light, but found that the organic product wasprincipally polychloro-cyclohexane. liaragher and Garner, J. A. C. S.43, 1715 (1921) reacted cyclohexane with between 50 and 75 per cent ofits molecular equivalent of chlorine under the inuence of light at atemperature between and C., but obtained cycloheXyl chloride in lessthan 55 per cent based on the cycloherrane consumed.

Because of such diliculties, cyclohexyl halides are usually prepared byreacting cyclohexanol with a desired hydrogen halide. This method,although giving rise to less byproduct formation than occurs in thehalogenation of cyclohexane, is objectionable from a manufacturing viewpoint in that cyclohexanol is a far more expensive starting materialthan cyclohexane soy rated from the halo-cyclohexane product andreturned to the reaction.

The invention also comprises other important features. For instance, wehave found that metal surfaces of equipment to be contacted with thereaction mixture may advantageously be coinposed of nickel, lead, orMonel metal. Surfaces of iron, boiler plate, Invar steel, etc., are cormroded appreciably by halogenated cyclohexane under the conditions ofoperation and the corrosion products direct the halcgenation towardformation of polyhalogenated products. Nickel, however, is attacked toslight extent, if at all. Monel metal is attacked only slightly and thecorrosion products do not influence appreciably the reaction between ahalogen and cyclohexane. Lead is at first corroded to limited extent,but the corrosion practically ceases after the reaction has proceededior a short time and the products of such corrosion appear to catalyzeintroduction of a single halogen atom into the cyclohexane nucleus.

We have also found in the manufacture of a cyclohexyl halide, that thepolyhalo-cycloliexane by-products may advantageously be used to scrubvaporized cyclohexane from the gaseous hydrogen halide evolved in thereaction.

In addition, We have devised a batch method for carrying out the cyclicprocess which, because of its simplicity, is well adapted to use eitherin the laboratory or on a manufacturing scale and also a continuous modeof operation which is better adapted for the large scale manufacture ofcyclohexyl halides.

The accompanying drawings illustrate certain of the various forms ofapparatus which may be employed in practicing the invention. Figure 1 ofthe drawings shows a simple form of apparatus which may be used whenoperating in batch manner. tinuous production of cyclohexyl halides inaccordance with the invention.

In Figure 1, numeral l indicates a, still provided with a distillingcolumn 2. Vapor line 3 leads from the top oi the column 2 to a condenserfz, from which a'conduit 5 for the condensate connects with the upperportion of a reaction cnamber 6. The latter is provided withv a chlorineinlet l which projects below the normal liquid level inside the chamber,an inlet 8 ior cycloliexane, and with a gas line 9, which connects witha vertical condenser ID having a vent il. Chamber S is also providedwith a source oi light, I2, e. g. a string of electric lights, encasedin a tube I3, of glass or other transparent Figure 2 shows apparatus forthe contop with a gas Vent I9.

vided at the bottom with the drains,` I and I6, v

respectively. v 1 l In Figure.2,.thelnumerals,l, 3, 4, 5, 6, 'I, 8, 9, l

I2, I3 and I4 vrepresent elements corresponding to the elementsdesignated by the same numerals in Figure l, except that in Figure 2,the still I is a continuous 'type including both a column and a heating4means (not shown) near the bottom thereof, the conduit 5 for return ofdistillate to reaction chamber 6 is provided with valved branch I6connecting with the top of still I, and the vapor line 9 leading fromthe top of chamber 6 connects with the lower portion of a scrubbingtower I8 which is provided at its The continuous still I of Figure 2 isprovided near its lower end with a line I 'I connecting with anothercontinuous still 2I. The latter is provided near its top with a vaporoutlet 22 which connects with a condenser 23. Condenser 23 is providedwith an outlet line 24 for withdrawing distillate from the system, butthe line 24 is provided with a valved branch 25 which connects with thetop of still 2| and per- 'mits return of a portion of the distillate tothe still for purpose of redux. Atthewbottom of still 2I is a conduit26whic`l1`"connect vwith a reservoir 2l and permits high boiling liquidto drain from the still to the reservoir. The latter is iitted at oneside with an overiiow drain 28 and near its bottom with a conduit 29which connects with a pump 30 which in turn is connected by means ofconduit 3l with a cooling device 32. A conduit 33 connects device 32with the upper part of scrubbing tower I8 and the latter is provided atits bottom with a drain line 20 which connects with the continuous stillI.

In the manufacture of cyclchexyl chloride using the apparatusillustrated in Figure l of the drawings, cyclohexane is charged intoreaction chamber 6 through inlet 8 until the still I is at leastpartially filled by overiiow from said chamber. Inlet 8 is then closedand the still I is put into operation, thereby causing circulation ofcyclohexane from the still to the reaction chamber E via column 2,conduit 3, condenser 4, and conduit 5, and back. into the still by wayof overflow line I4. The electric lights I2 are illuminated and chlorineis introduced continuously through inlet I into chamber 6. lThe rate ofchlorine input is balanced against the rate of cyclohexane circulationso that not more than 0.3 mole, preferably 0.1 mole or less, of chlorineenters chamber 6 per mole of cyclohexane entering said chamber bydistillation from the still I. The chlorination starts at roomtemperature after which the temperature usually rises spontaneouslytobetween 40 and 80 C. The exact temperature employed is of littleconsequence. Hydrogen chloride gas generated by the reaction passesthroughconduit 9 intov an eiiclent condenser I0 wherein cyclohexanewhich maybe vaporized with thegas is condensed and permitted to flowback in'tochamber 6. The hydrogen chloride is vented through outlet IIinto suitable receivers wherein it is collected as byproduct of thereaction. During operation in such manner, a liquid mixture ofcyclohexyl chloride and unreacted cyclohexane continuously overflowsfrom reaction chamber E to the still I which is operated in such manneras to dstill the cyclohexane back into chamber 6, but retain thecyclohexyl chloride. Toward the end of` the chlorination, the distillingtemperature tion liquor isremoved 'froml the'system through drains I5and I6 and fractionally distilled to obta'in the cyclohexyl-chlorideproduct in puried condition.

The apparatus shown in Figure 2 of the drawings operates on the samegeneral principal as that shown in Figure l, although the details ofoperation are quite diiierent. In using the apparatus of Figure 2,chlorine and cyclohexane are introduced continuously into reactioncharnuber B through inlets l and 8, respectively. The hydrogen chloridegas generated leaves chamber 6 through conduit 9 from which it entersscrubbing tower I8, wherein it is scrubbed with poly--chloro-cyclohexanes to remove any vapor-ized cyclohexane. and nally isvented through outletl I 9 into suitable receivers. The reaction liquoverows into continuous still I which is erated in such manner thatcyclohexane is tilled off through line 3, condenser 4, and line 5 backinto the reaction chamber 6 and chlorinated cyclohexane drains'continuously through line 'I1 into another continuous still 2I. Duringoperation, the rates of chlorine and cyclohexane input through inlets 1and 8 and the rate of distillation of cyclohexane from still I tochamber 6 are controlled so that the molecular ratio of chlorine tocyclohexane 'entering chamber 6 does not exceed 0.3 and is preferablyless than 0.1. In still 2|, the chlorinated cyclohexane is fractionatedto separate the cyclohexyl chloride product which passes from the stillthrough vapor line 22, condenser 23 and outlet 24. A portion of thedistillate is returned to the still through line 25 for purpose ofreflux. Polychloro-cyclohexane drains continuously from still 2| throughliquor line 25 into storage tank 2l from which itis pumped by means ofpump 30 through lines 29 and 3|, cooler 32 and line 33 into the top ofscrubbing tower I8 wherein it serves to extract vaporized cyclohexanefrom the hydrogen chloride evolved from the reaction mixture. Thepolychloro-cyclohexane entering tower I8 is cooled preferably below 20C. in order to obtain eicient scrubbing. The scrubbing liquor drainsfrom tower lI8 through conduit 20 into still l wherein the dissolvedcyclohexane is distilled therefrom. As polychloro-cyclohexaneaccumulates beyond the amount required for operation, it overflows fromthe system through outlet 20.

Using the apparatus of Figure 1 or Figure 2 of the drawings, theinvention as hereinbefore described may be applied to the production ofcyclohexyl bromide by substituting bromine for chlorine as thehalogenating agent. If desired, it may also be applied to the productionof a given polyhalo-cyclohexane, e. g, dichloro-cyclohexane,trichloro-cyclohexane, or dibromo-cyclohexane, etc., in good yield bymerely controlling the distillation of the crude reaction liquor so thatmaterial of boiling point below that of the desired product iscontinuously distilled back into the reaction chamber, but the productdesired is not returned to said chamber.

Although light is preferred as a catalyst for the halogenation, anyhalogenation catalyst which distills at a temperature below the boilingpoint of the desired product may be used. For v instance, we havesuccessfully produced cyclohexyl chloride without aid of light by usingphosphorus tri-chloride as the catalyst. The phosphorus tri-chloridecirculated along with the unreacted cyclohexane and was therebycontinuously returned to the reaction.

When light is used as the catalyst. it must, of course, be employed inintensity sufficient to promote rapid reaction. We have observed thatlight of wave length between 5200 and 5400 Angstrom units is mosteiective as a catalyst for the chlorination of cyclohexane.

The following examples illustrate certain Ways in which the principle ofthe invention has been applied, but are not to be construed as limitingthe invention.

Example I Employing laboratory apparatus similar in construction to thatillustrated in Figure 1 of the drawings, 1680 grams (20 moles)ofcyclohexane was reacted with 1120 grams (7.0 moles) of bromine duringa period of 20.5 hours. During reaction, the bromine was introduced tothe reactor at a constant rate of approximately 55 grams (0.34 mole) ofbromine per hour and unreacted cyclohexane was cycled through thereactor at such rate that approximately 20 moles of cyclohexane enteredthe reactor for each mole of bromine entering the same. The reaction wascatalyzed by light from a 100 watt electric light bulb placed at adistance of about 3 inches from` the reaction mixture. The reactedmixture was then fractionally distilled, there being separated 1180grams (14.05 moles) of unreacted cyclohexane, 603 grams (3.7 moles) ofsubstantially pure cyclohexyl bromide, and 132.9 grams of more highlybrominated products. Of the brominated products obtained from thereaction, approximately 86 per cent by weight was cyclohexyl bromide.

Example 2 considerably above the boiling point of cyclohexane andapproaching that of cyclohexyl chloride, by which time more than half ofthe chlorine theoretically requiredto convert all of the cyclohexanetocyclohexyl chloride had been re acted. The chlorination was then stoppedand the product was separated by distillation. The yield of cyclohexylchloride was approximately 94.5 per cent of theoretical, based on thecyclohexane reacted.

Example 3 948 grams (8.0 moles) of cyclohexyl chloride was cycledthrough the apparatus employed in Example 1 at such rate that 20 grams(0.17 mole) of cyclohexyl chloride passed into the reactor per minute.Chlorine was admitted to the reactor at a rate of about 0.70 grams(0.0099 mole) per minute. During reaction, the mixture within thereactor was illuminated with light from a watt electric light bulbplaced at a distance of about 2 feet from said mixture and the latterwas maintained at a temperature between about 50 and 55 C. Chlorinationwas continued until the material passing from the still had a boilingpoint of 152 C. The mixture was removed from the apparatus and blownwith air to remove hydrogen chloride therefrom. It was then completelyneutralized with anhydrous sodium carbonate, filtered, and fractionallydistilled. There was obtained 411 grams (3.47 moles) of unreactedcyclohexyl chloride, 577 grams (3.64 moles) of a mixture of lsomericdichloro-cyclohexanes boiling between and- 200o C. at atmosphericpressure, and 118 grams of more highly chlorinated products. Of thereaction products, 83 per cent by weight consisted ofdichloro-cyclohexane.

Other modes of applying the principle of the invention may be employedinstead of those explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

We therefore particularly point out and distinctly claim as ourinvention:

1. In a method wherein a halogen selected from the class consisting ofchlorine and bromine is reacted with liquid cyclohexane to produce acyclohexyl halide, a polyhalo-cyclohexane and gaseous hydrogen halide,the step of scrubbing the hydrogen halide with the polyhalocyclohexaneto extract vaporized cyclohexane therefrom.

2. In a continuous method for the production of a cyclohexyl halide, thesteps which consist in introducing cyclohexane and not more than 0.3 ofits molecular equivalent of a halogen selected from the class consistingof chlorine and bromine, into admixture, exposing the mixture to actiniclight while contacting it with metal surfaces consisting only of asubstantially inert metal, whereby the cyclohexane is halogenated,continuously withdrawing a portion of the reaction liquor and distillingthe withdrawn liquor while in contact with metal surfaces consistingonly of a substantially inert metal to distill oi a cyclohexane fractionsuitable for recycling in the process and leave a mixture of chlorinatedcyclohexanes, distilling the chlorinated cyclohexanes to separate, acyclohexyl halide fraction,

and a polyhalo-cyclohexane fraction, and employing the last mentionedfraction as an agent for extracting vaporize'd cyclohexane from thegaseous hydrogen halide evolved by the reaction.

EDGAR C. BRI'I'I'ON. RALPH P. PERKINS.

